The OAIC Body Composition Research Core will provide expertise and support to all affiliated research studies involved in the precise in vivo measurement of body composition, focusing specifically on skeletal muscle mass and composition, fat mass and distribution, and bone mineral density. The Body Composition Core will play a pivotal role in the OAIC, interacting closely with all other Cores. The specific aims of the Body Composition Core are: (1) to supplement independently funded studies to include relevant body composition measurements; (2) to support Pilot and Research Development Studies that include body composition measurements; (3) to collaborate with other Cores in the development of new, multidisciplinary projects that translate between basic and clinical research; (4) to develop new body composition methodologies for application in the OAIC; and (5) to train new investigators in the application of body composition methods in gerontologic research. In conjunction with other Cores, the Body Composition Core will also pursue the following scientific aims, which will advance the overall theme of the OAIC: (a) to refine clinical criteria for defining sarcopenia and sarcopenic-obesity; (b) to determine what associations exist between biological, genetic, co-morbid, psychosocial, and behavioral factors and sarcopenia and arcopenic-obesity; (c) to determine what associations exists between magnetic resonance imaging/spectroscopy measures and muscle volume, muscle composition, and muscle function.